There have been a lot of mono/poly people come through these parts with similar concerns. My bf for one. He has always called himself my secondary, but he is only in terms of no shared assets. He lives with my husband and I and contributes to the house, but if my husband and I were to split we would have to sort out assets, bf and I don't have to do that. That is the only basis for primary/secondary that makes sense to me.
Check out some threads by doing a tag search here for "mono/poly." Could be useful.
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